Catalyst regeneration

ABSTRACT

The regeneration of cracking catalyst containing both manganese and antimony in a temperature range of 1260°-1280° F. has been found to result in unexpected sharp maximum of the CO 2  /CO ratio in the regenerator off-gas.

This is a division of application serial No. 117,927, filed Feb. 4,1980, now U.S. Pat. No. 4,335,021, 6/15/82.

This invention relates to the regeneration of catalysts that are usefulfor cracking hydrocarbons. In another aspect, this invention relates toa hydrocarbon cracking process.

BACKGROUND

It is well known in the art that cracking of hydrocarbons with silica orsilica/alumina base catalysts produces coke on such catalysts which canbe burned off. One of the problems arising in the cracking step consistsin the detrimental effects brought about by such metals as nickel,vanadium, and iron contained in many hydrocarbon feedstocks. Thesemetals cause production of hydrogen and coke. A problem arising in thecatalyst regeneration step resides in the fact that the ratio of carbondioxide to carbon monoxide normally decreases with increasingtemperature. Therefore, although high temperatures are a desirableprocess parameter, it is not feasible to increase the temperature sincethis would lead to a further decrease in an already low carbon dioxideto carbon monoxide ratio in the off gases.

It has been claimed in the art that antimony, bismuth and manganeseadded to a cracking catalyst increased the carbon dioxide to carbonmonoxide ratio. The art gives examples utilizing antimony and bismuth.There is a continuing interest in increasing the CO₂ /CO volume ratio ina catalyst regeneration step.

STATEMENT OF THE INVENTION

It is thus one object of this invention to provide a process forcombusting carbonaceous materials on catalyst particles with a highcarbon dioxide to carbon monoxide ratio.

Another object of this invention is to provide a cracking processincluding a catalyst regeneration step in which process both thedetrimental effects of metals such as nickel, vanadium, and iron aremitigated and the CO₂ /CO ratio of the regeneration off gases ismaximized.

These and other objects, advantages, details, and features of thisinvention will become apparent to those skilled in the art from thefollowing detailed description thereof and the appended claims.

In accordance with this invention it has now been found thatcarbonaceous material accumulated on cracking catalyst can be burned offwith a very high CO₂ /CO volume ratio in the produced gases if thecatalyst contains both antimony and manganese and if the combustion iscarried out in a very limited temperature range of 1260°-1280° F.

Thus, in accordance with one embodiment of this invention a process forcombustion of carbonaceous material is provided for.

In accordance with another embodiment of this invention a crackingprocess is provided for in which a hydrocarbon feedstock is cracked in acracking zone with a cracking catalyst containing manganese andantimony; the cracking catalyst containing manganese and antimony isthen subjected to a regeneration by contacting it with a free oxygencontaining gas at a temperature of 1260°-1280° F.; thereafter theregenerated cracking catalyst is again utilized for the cracking step.

It has surprisingly been found that manganese and antimony togetherresult in a synergistic improvement and increase of CO₂ /CO ratio of theregenerator off-gas when these metals are present on a catalyst in acracking/regeneration cycle. Manganese and antimony are passivatingagents for the contaminating metals such as nickel, vanadium and ironcausing a reduction of hydrogen and coke produced during the crackingprocess and also have the additional function of strongly increasing theCO₂ /CO ratio as described. Antimony or a compound thereof and manganeseor a compound thereof together in addition to their metals passivationeffect cause an increase in the carbon combustion from catalyst duringthe regeneration thus releasing more heat in the regenerator. At thesame time, the quantity of carbon monoxide released is reduced. Thelatter is of particular significance where a portion or all of theregenerator off-gases are released to the atmosphere.

FEEDSTOCKS

Hydrocarbon feedstocks to the catalytic cracking process of thisinvention encompass all the oils usually contemplated for catalyticcracking processes. The initial boiling point of the hydrocarbonfeedstocks envisaged generally is above 204° C. Examples of suchfeedstocks include gas oils, fuel oils, cycle oils, slurry oils, toppedcrudes, shale oils, oils from tar sands, oils from coal or coalliquefaction, and mixtures of such oils. The hydrocarbon feedstockscontemplated for this invention are those containing significantconcentrations of contaminating metals such as vanadium, iron andnickel. Since these contaminating metals tend to concentrate in theleast volatile fractions of these feedstocks, cracking of heavy oils isone of the most difficult procedures in the art of hydrocarbon crackingand one of the most important applications of this invention.

The concentration of manganese and antimony on the cracking catalyst canbe related to the total effective metals content of the feedstock asshown in the following table.

    ______________________________________                                        Total Effective Metals                                                                        Mn + Sb Concentration                                         in Feedstock (ppm)*                                                                           in Catalyst, Wt. %**                                          ______________________________________                                         1-40           0.01-0.6                                                       40-100         0.05-0.8                                                      100-200         0.1-1                                                         200-300         0.15-1.5                                                      300-800         0.2-2                                                         ______________________________________                                         *"Total effective metals" is the sum of the concentration of vanadium and     iron plus four times the concentration of nickel and copper.                  **Based on the weight of catalyst prior to addition of manganese and          antimony.                                                                

CRACKING CATALYSTS

Cracking catalysts are compositions useful for cracking hydrocarbons inthe absence of added hydrogen. They are used to convert the hydrocarbonfeedstocks having a normal boiling point above 204° C. to more volatilecompounds, e.g., gasoline and light distillates. Generally they containsilica or silica/alumina, frequently in association with zeoliticmaterials. These zeolitic materials can be naturally occurring orsynthetic, and they usually are subjected to ion exchange treatment toimprove the activity of the catalyst in which they are incorporated, byreplacing at least part of the original alkali metal or alkaline earthcations with rare earth element cations and hydrogen ions, or with ionscapable of conversion to hydrogen ions.

Unused cracking catalyst contains essentially no vanadium, iron, andnickel. Their concentrations in unused catalyst will not exceed 0.06weight percent vanadium, 0.8 weight percent iron, and 0.02 weightpercent nickel. These concentrations refer to the total weight of theunused catalyst, but excluding added manganese and antimony treatingagents.

TREATING AGENTS

Manganese that is used to treat the contaminated catalyst can be addedas the elemental metal, or it can be applied as a compound of manganese.Suitable compounds include manganese oxides, such as manganese monoxideMnO, manganese sesquioxide Mn₂ O₃, manganous-ic oxide Mn₃ O₄, andmanganese dioxide MnO₂, manganese sulfides such as manganous sulfide MnSand manganic sulfide MnS₂, salts of carboxylic acids such as manganeseacetate Mn(C₂ H₃ O₂)₂, and manganese oxalate MnC₂ O₄, salts of mineralacids such as manganese nitrate Mn(NO₃)₂, manganese sulfate MnSO₄ andMn₂ (SO₄)₃, and manganese halides such as manganese fluorides andmanganese chlorides, and manganese phosphates such as manganeseorthophosphate Mn₃ (PO₄)₂ and manganese ammonium phosphate Mn(NH₄)PO₄.

The second necessary ingredient in this invention in addition tomanganese is antimony. Elemental antimony, inorganic antimony compoundsand organic antimony compounds or mixtures of such antimony sources canbe utilized.

Examples of some inorganic antimony compounds which can be used includeantimony oxides such as antimony trioxide, antimony tetroxide, andantimony pentoxide; antimony sulfides such as antimony trisulfide andantimony pentasulfide; antimony selenides such as antimony triselenide;antimony tellurides such as antimony tritelluride; antimony sulfatessuch as antimony trisulfate; antimonic acids such as metaantimonic acid,orthoantimonic acid and pyroantimonic acid; antimony halides such asantimony trifluoride, antimony trichloride, antimony tribromide,antimony triiodide, antimony pentafluoride and antimony pentachloride;antimonyl halides such as antimonyl chloride and antimonyl trichloride;antimonides such as indium antimonide; and the like. Of the inorganicantimony compounds, those which do not contain halogen are preferred.Although organic antimony compounds for use in the preparation of theantimony/manganese-containing catalysts preferably contain about 3 toabout 54 carbon atoms for reasons of economics and availability, organicantimony compounds outside this range are also applicable. Thus, organicpolymers containing antimony can be employed as the organic antimonycompound. In addition to carbon and hydrogen, the organic antimonycompound can contain elements such as oxygen, sulfur, nitrogen,phosphorus or the like. Examples of some organic antimony compoundswhich can be used in the preparation of theantimony/manganese-containing catalysts include antimony carboxylatessuch as antimony triformate, antimony trioctoate, antimony triacetate,antimony tridodecanoate, antimony trioctadecanoate, antimonytribenzoate, and antimony tris(cyclohexanecarboxylate); antimonythiocarboxylates such as antimony tris(thioacetate), antimonytris(dithioacetate) and antimony tris(dithiopentanoate); antimonythiocarbonates such as antimony tris(O-propyl dithiocarbonate), antimonycarbonates such as antimony tris(ethyl carbonate);trihydrocarbylantimony compounds such as triphenylantimony;trihydrocarbylantimony oxides such as triphenylantimony oxide; antimonysalts of phenolic compounds such as antimony triphenoxide; antimonysalts of thiophenolic compounds such as antimony tris(thiophenoxide);antimony sulfonates such as antimony tris(benzenesulfonate) and antimonytris(p-toluenesulfonate); antimony carbamates such as antimonytris(diethylcarbamate); antimony thiocarbamates such as antimonytris(dipropyldithiocarbamate), antimony tris(phenyldithiocarbamate) andantimony tris(butylthiocarbamate); antimony phosphites such as antimonytris(diphenylphosphite); antimony phosphates such as antimonytris(dipropyl phosphate); antimony thiophosphates such as antimonytris(O,O-dipropyl thiophosphate) and antimony tris(O,O-dipropyldithiophosphate) and the like. The last compound is also known asantimony tris(O,O-dipropyl phosphorodithioate), and is the presentlypreferred source of antimony, due in part to its solubility inhydrocarbons and its commercial availability. Mixtures of any two ormore applicable substances comprising antimony can be employed.

The cracking catalyst of this invention can be one that during thecracking process has become contaminated with metals such as vanadium,iron and/or nickel and thereafter has been provided with manganese andantimony or respectively compounds of those metals to at least partiallypassivate the detrimental metal. It is, however, also within the scopeof this invention that the combination of manganese and antimony orcompounds thereof are already present on the unused cracking catalyst.The combination of antimony and manganese on the cracking catalystcauses a passivation of the metals or respectively prevents at leastsome of the detrimental effects of metals such as vanadium, nickel, andiron otherwise occuring. Furthermore, the combination of the two metals,manganese and antimony results in the surprising effect of verysignificantly increasing the CO₂ /CO ratio in the off-gases of thecatalyst regenerator.

The cracking catalyst of this invention contains generally about 0.01 to8 weight percent, preferably about 0.02 to 2 weight percent ofmanaganese and about 0.01 to 8 weight percent, preferably about 0.02 to2 weight percent of antimony. These concentrations are expressed as theelemental metal and are based on the weight of the total catalyst aftertreating, i.e. on the weight of the catalyst and the added metals as 100percent. The weight ratio of manganese to antimony utilized on thecatalyst of this invention generally is in the range of 10:1 to 1:10,preferably in the range of 2:1 to 1:2.

A variety of methods may be used to apply the manganese and antimonytreating agents to the catalyst. They may be added to the crackingcatalyst as finely divided solids and dispersed by rolling, shaking,stirring, etc. Another possibility is to dissolve the Mn and Sb sourcematerials in a suitable solvent, aqueous or organic, and to use theresulting solution to impregnate the cracking catalyst followed byremoval of the solvent. Alternatively the Mn and Sb source may bedissolved or dispersed in the hydrocarbon feedstock to the crackingprocess where the manganese and antimony are deposited on and retainedby the catalyst.

PROCESS CONDITIONS

In the process of this invention catalytic cracking of feedstocks iseffected either in a fixed catalyst bed or with a fluidized catalystoperation. The latter is preferred. Specific conditions in the crackingzone and the regeneration zone of a fluid catalytic cracker depend uponthe feedstock used, the condition of the catalyst, and the productsought. In general conditions in the cracking zone include:

Temperature: 427°-649° C. (800°-1200° F.)

Time: 1-40 seconds

Pressure: 10 kPa to 21 MPa (0.1 to 205 atm.)

Catalyst/oil ratio: 3/1 to 30/1, by wt.

Conditions in the regeneration zone generally include:

Temperature: 1260°-1280° F.

Time: 2-40 minutes

Pressure: 10 kPa to 21 MPa (0.1 to 205 atm.)

Air rate (at 16° C., one atm.): 100-250 ft.³ /lb. coke, or 6.2-15.6 m³/kg coke

The following examples are intended to illustrate the invention anddescribe further preferred features without undue limitation of theinvention.

EXAMPLE I

A commercial fluid cracking catalyst comprising amorphous silica/aluminaand rare earth cation-exchanged zeolite, which had been used in acommercial fluid catalytic cracker until it had attained equilibriumcomposition with respect to metals accumulation (catalyst was beingremoved from the process system at a constant rate) was used todemonstrate the effect of being treated with both manganese andantimony. Table I summarizes the composition as determined by analysis,and some pertinent physical properties of this catalyst, designatedcataylst O.

                  TABLE I                                                         ______________________________________                                        Surface area, m.sup.2 /g                                                                        74.3                                                        Pore vol., ml/g   0.29                                                        Composition, wt. %                                                            Aluminum          21.7                                                        Silicon           24.6                                                        Sodium            0.39                                                        Vanadium          0.60                                                        Iron              0.90                                                        Nickel            0.38                                                        Cerium            0.40                                                        Carbon            0.06                                                        ______________________________________                                    

Portions of catalyst O were used to prepare four catalysts containingmanganese and/or antimony as follows.

Catalyst A was prepared by adding 0.4434 g of powdered MnS and 0.6114 gof powdered Sb₂ (SO₄)₃ to 35.0 g of dry catalyst O in a tubular quartzreactor. These components were mixed by fluidization for 10 minutes atroom temperature with nitrogen, then heated to 482° C. whilefluidization with nitrogen continued. Nitrogen was replaced withhydrogen and the temperature was increased to 649° C. Nitrogen replacedhydrogen and the catalyst was fluidized for five minutes at temperatureto purge the reactor after which the catalyst was fluidized with air for15 minutes at that temperature. Catalyst A contained 0.79 weight percentof both manganese and antimony by calculation.

Catalyst B was prepared by adding 0.3991 g of powdered MnS and 0.5503 gof Sb₂ (SO₄)₃ to 36 g of catalyst O. The components were mixed andconditioned during fluidization just as described for catalyst A.Catalyst B contained 0.69 weight percent of both manganese and antimonyby calculation.

Catalyst C was prepared by adding 0.4434 g of powdered MnS to 35 g ofcatalyst O. The components were mixed and conditioned duringfluidization just as described for catalyst A. Catalyst C contained 0.79weight percent of manganese by calculation.

Catalyst D was prepared by adding 0.624 g of Sb₂ (SO₄)₃ to 35 g ofcatalyst O. The components were mixed and conditioned duringfluidization just as described for catalyst A. Catalyst D contained 0.79weight percent of antimony by calculation.

Catalysts O and A were evaluated to crack a West Texas topped crude oil.Prior to that run catalyst A was aged by being subjected to ten cyclesof the following treatment after receiving the conditioning alreadydescribed. The catalyst at about 482° C. was fluidized with nitrogen forone minute, then heated to about 510° C. during two minutes whilefluidized with hydrogen, then maintained at 510° C. for one minute whilefluidized with nitrogen, then heated to about 649° C. for 10 minuteswhile fluidized with air, and then cooled to about 482° C. during 0.5minutes while fluidized with air. After 10 such cycles it was cooled toroom temperature while being fluidized with nitrogen and was tested.Catalysts O and A were tested in fluidized bed reactors at 510° C. andatmospheric pressure using 0.5 minute cracking periods with interveningregeneration periods at about 649° C.

Pertinent properties of the topped West Texas crude oil used in theseruns are tabulated in U.S. Pat. No. 4,111,845 at column 8.

A series of runs was made in which the catalyst/oil ratio was varied toobtain the desired range of conversions. Gas and liquid products wereanalyzed by GLC and the reactor was weighed to determine coke. A smoothcurve was obtained from the data points and results at 75 volume percentconversion of the feed are presented in Table III.

                  TABLE III                                                       ______________________________________                                                                   Scf H.sub.2 /bbl                                   Cata- Cat./Oil  Coke, Wt. %                                                                              Feed    Gasoline,                                  lyst  Wt. Ratio of Feed    Converted                                                                             Vol. % of Feed                             ______________________________________                                        O     7.4       16.4       800     54.8                                       A     6.15      12.6       360     59.0                                       ______________________________________                                    

The presence of 0.79 wt. % each of manganese and antimony on the usedcracking catalyst decreased the coke produced by 23%, decreased thehydrogen produced by 55%, and increased the yield of gasoline by 7.7%.

EXAMPLE II

Catalysts O, A, B, C, and D all were used separately to crack the toppedcrude in exactly the manner described in example I, 0.5 minutes at 510°C. and atmospheric pressure. After addition of the oil had ceased,fluidization of the catalyst with nitrogen continued for 10 minutes tostrip hydrocarbons from the reactor. Coked catalysts were regeneratedwith air and the CO₂ /CO ratio in the off-gas was determined bymeasuring their concentrations by GLC. Portions of the off-gas werecollected by water displacement in receivers large enough to contain theoff-gas produced in several minutes. Regeneration was generally completewithin 40 minutes, and, when it was desired, several samples of off-gaswere obtained during a single regeneration. These samples were alwayscollected during the first 20 minutes of oxidation; the concentration ofcarbon oxides in the regeneration off-gas was constant during that partof the process. A thermocouple in the bed of fluidized catalyst beingregenerated indicated its temperature which changed with time because ofthe heat liberated during regeneration. In some runs the air forregeneration was saturated with water vapor at about 24° C. before beingintroduced into the reactor; in other runs the air was not humidified.This difference in treatment is not believed to have affected the CO₂/CO ratio in the off-gas. Table IV summarizes pertinent conditions andresults from regeneration of coked catalysts O, A, B, C, and D asdescribed. These data have also been plotted to show the relationbetween CO₂ /CO mole ratio and the regeneration temperature in FIGS.1-5.

The figures show that the CO₂ /CO ratio from regenerating untreatedcatalyst O declines monotonically from about 5 to about 2 as thetemperature of regeneration increases from about 850° to about 1350° F.In contrast catalysts A and B, both of which contain manganese andantimony in equal concentrations, show unexpected activity to oxidizecarbon more completely in the temperature range of about 1260° to 1280°F. Data from catalyst A were obtained in runs that span a large fractionof the temperature range generally used to regenerate FCC catalyst.Catalyst B, prepared subsequently, was used in runs to define in detailthe temperature range disclosed by catalyst A. Regeneration off-gas fromit showed essentially identical CO₂ /CO ratios versus regenerationtemperature, and confirm that the particularly effective temperaturerange is about 1260°-1280° F.

Catalyst C, treated with manganese only, and which is not a part of thisinvention, suggests that at about 1050° F. it is particularly effectivefor carbon oxidation to carbon dioxide. Catalyst D, treated withantimony only, in two runs showed anomalously high CO₂ /CO ratios atabout 1250° F., but the ratio is substantially smaller than thatobtained when antimony was combined with manganese at about the sametemperature.

                  TABLE IV                                                        ______________________________________                                                      Air        Regeneration                                                                              Mole Ratio                               Catalyst                                                                             Run    Humidified?                                                                              Temp., °F.                                                                         CO.sub.2 /CO                             ______________________________________                                        O       1     Yes        1225        2.83                                     O             Yes        1219        2.74                                     O       2     No         1218        2.81                                     O             No         1190        3.09                                     O       3     Yes        1378        2.61                                     O             Yes        1100        3.47                                     O             Yes        1022        3.83                                     O       4     Yes        1253        3.61                                     O             Yes        1265        2.29                                     O             Yes        1281        2.21                                     O       5     Yes        1155        4.05                                     O             Yes        1173        2.62                                     O             Yes        1335        2.07                                     O       6     Yes         852        5.14                                     O             Yes         875        5.31                                     O             Yes         905        4.93                                     O             Yes         912        4.13                                     A        7*   Yes        1260        9.65                                     A       8     Yes        1012        4.67                                     A             Yes        1110        2.85                                     A             Yes        1356        3.57                                     A       9     Yes        1092        4.10                                     A             Yes        1275        8.13                                     A             Yes        1275        7.33                                     A             Yes        1180        3.36                                     A      10     Yes        1320        5.31                                     A             Yes        1212        2.92                                     A             Yes        1055        3.62                                     A      11     Yes        1272        8.31                                     A             Yes        1262        3.44                                     A             Yes        1266        3.19                                     B      12     No         1268        9.92                                     B             No         1266        5.37                                     B             No         1264        4.48                                     B      13     No         1263        8.22                                     B             No         1255        4.55                                     B             No         1250        4.46                                     B      14     No         1260        7.08                                     B             No         1266        4.33                                     B      15     No         1271        6.83                                     B             No         1277        4.53                                     B             No         1283        4.49                                     B             No         1287        5.69                                     B      16     No         1257        7.49                                     B             No         1253        4.58                                     B             No         1247        4.81                                     B             No         1239        5.11                                     B      17     No         1268        3.88                                     B      18     Yes        1262        7.17                                     B             Yes        1264        3.54                                     B      19     No         1263        7.04                                     B             No         1265        15.93                                    B      20     No         1271        5.21                                     B             No         1272        9.34                                     B             No         1279        12.34                                    B      21     No         1258        6.03                                     B             No         1260        7.98                                     B             No         1260        14.81                                    C       22*   Yes        1257        3.83                                     C             Yes        1186        3.17                                     C             Yes        1006        3.52                                     C      23     Yes        1060        5.39                                     C             Yes        1237        3.18                                     C             Yes        1350        3.87                                     C             Yes        1108        3.31                                     C      24     Yes        1042        5.97                                     C             Yes        1253        3.05                                     C      25     Yes        1046        6.75                                     C             Yes        1278        3.39                                     C             Yes        1305        3.31                                     D      26     Yes        1239        5.41                                     D             Yes        1187        3.01                                     D             Yes        1113        3.51                                     D             Yes        1018        4.02                                     D             Yes        1266        2.47                                     D      27     Yes        1250        2.44                                     D             Yes        1259        2.68                                     D             Yes        1260        4.05                                     D             Yes        1280        2.08                                     D             Yes        1347        2.03                                     ______________________________________                                         *Cracking reaction at 1050° F. (566° C.)                   

Reasonable variations and modifications apparent to one skilled in theart can be made in this invention without departing from the spirit andscope thereof.

I claim:
 1. A process comprising(a) contacting a hydrocarbon feedstockwith a silica or silica/alumina based cracking catalyst in a crackingzone and under cracking conditions to produce a cracked hydrocarbonproduct, said cracking catalyst containing both manganese and antimonyin a quantity to at least mitigate the detrimental effects of metalssuch as nickel, vanadium, and iron in the feedstock, and in a ratio ofantimony to manganese in the range of 10:1 to 1:10, (b) removing saidcracked hydrocarbon product from said cracking catalyst, (c) contactingsaid cracking catalyst with free oxygen at a temperature in the range of1260° to 1280° F. such as to burn off at least a portion of thecarbonaceous material accumulated on said cracking catalyst during thecracking step and converting it to CO₂ and CO in a high ratio of CO₂/CO. (d) repeating these steps a plurality of times.
 2. A process inaccordance with claim 1 comprising(a) removing said cracking catalystfrom said cracking zone, (b) stripping hydrocarbons from said crackingcatalyst so removed, (c) contacting the so stripped cracking catalyst ina regeneration zone with free oxygen, (d) stripping free oxygen from theso regenerated cracking catalyst, (e) recycling the regenerated andstripped cracking catalyst to said cracking zone and repeating thecycle.
 3. A process in accordance with claim 1 comprising adding bothmanganese and antimony or compounds of these metals to the crackingcatalyst.
 4. A process in accordance with claim 3 wherein manganese andantimony or respectively their compounds are added to the crackingcatalyst by incorporating an antimony source and a manganese source tothe hydrocarbon feedstock.